[SystemZ] Improve handling of Select pseudo-instructions

If we have LOCR instructions, select them directly from SelectionDAG
instead of first going through a pseudo instruction and then using
the custom inserter to emit the LOCR.

Provide Select pseudo-instructions for VR32/VR64 if we have vector
instructions, to avoid having to go through the first 16 FPRs
unnecessarily.

If we do not have LOCFHR, prefer using LOCR followed by a move
over a conditional branch.

llvm-svn: 331191